In recent years, the use of a digital still camera (in the following, referred to as DSC) allowing a user to check a captured image immediately has been expanding rapidly. As a lens barrel for this DSC, a so-called collapsible lens barrel, which can be made shorter when not in use, generally is adopted in view of its portability when not in use.
The collapsible lens barrel generally includes a collapsing mechanism in which a cam pin is allowed to mate with a cam groove so as to drive a lens frame and a lens group. In such a collapsing mechanism, when an external force is applied, the demating of the cam pin from the cam groove has to be prevented as it makes a camera main body unworkable. For example, JP 2002-90611 A discloses a mechanism for preventing a cam pin from demating from a cam groove as described in the following. That is, an outer peripheral surface of a cam ring is provided with a cam groove and a demating prevention groove extending along this cam groove, and an inner peripheral surface of a first lens frame is provided with a tapered cam follower and a cylindrical roller member that are inserted into the cam groove and the demating prevention groove, respectively. In this way, wall surfaces of the demating prevention groove facing each other and the roller member come into contact with each other when an external force is applied, making it possible to prevent the tapered cam follower sliding in the cam groove from demating from the cam groove.
However, in the conventional collapsible lens barrel described above, since the tapered cam follower sliding in the cam groove and the roller member moving inside the demating prevention groove have different shapes, two kinds of components are needed as the cam pins. Accordingly, the number of components increases, and the management thereof is complicated. Moreover, although these components are both small and have a slight difference in shape, there is a problem of complicated assembly. For example, the cam ring and the first lens frame cannot be assembled if these components are attached reversely at the time of the attachment to the first lens frame.